The present invention relates to a lighting control method and a lighting control apparatus of a light source in an image forming apparatus, and more particularly to a method and apparatus for controlling the timing to cause a light source to light in an image forming apparatus, wherein, by causing the light source which reciprocates for a prescribed number of times to light while the light source goes on, a reflected light from an original document is obtained by illuminating a sheet of original document, and based on such reflected light, an image is formed on a plurality of papers which is conveyed through a paper conveying section.
There has conventionally been provided an electrophotographic copying apparatus which is a kind of an image forming apparatus, wherein if a reproducible large sized original document is used, it is possible to prevent danger involved in moving the original document table and increased burden in a driving system for large sized original document table, and it is possible to install a document feeder in the apparatus, in which a transparent plate for placing an original document thereon is fixed so as to illuminate all over the surface of the original document by causing the light source to move reciprocatingly under the transparent plate.
In such a light source movable type electrophotographic copying apparatus, a location some distance away from one end of the transparent plate is made a home position of the light source, the light source is caused to turn on continuously during a going period in which the light source moves from the home position as a starting point, and the light source is caused to turn off continuously during a returning period in which the light source moves to the home position as a terminal.
Therefore, by accomplishing sequentially a necessary number of going motion of the light source while it is turned on and returning motion of the light source while it is turned off, it is possible to obtain continuously a plurality of number of sheets of reproduction with respect to one original document (continuous copying mode).
In an electrophotographic copying apparatus having the above constitution, in order to make the size of the body of the electrophotographic copying apparatus as small as possible, the distance between the home position and the end of the transparent plate is set to as small a distance as possible, so that the light source is caused to start to turn on while the light source is stopping at the home position and the light source is caused to move after a prescribed time has elapsed to stabilize the light source after it is turned on. Therefore, it is so arranged that the light source gives forth the light stably when the illumination of the original document on the transparent plate is started.
However, because the time the light source is stopping at the home position is long and as a result thereof the start of the paper conveying toward a photoreceptor from a registration roller is delayed, there exists a problem that it is not possible to improve the copying speed when continuous copying is necessary. In addition, because the time the light source is turned on in the neighbourhood to the home position is long, there also exists a problem that considerable temperature rise is caused in such area.
Especially, when a number of paper feeding cassette are stacked one upon another, the time required to convey paper to the registration roller varies, and if the light source is set to turn on according to the shortest time required to convey the paper from the paper feeding cassette to the registration roller, the light source will be turned on for a long time in case the time required for paper feeding is long and the temperature rise becomes all the more noticeable.
Furthermore, an electrophotographic copying apparatus capable of detecting a size of an original document is used, in which an optical system goes on to expose a portion where the original document is placed according to the detected size of the original document and returns back. In such an electrophotographic copying apparatus, for instance, a reducing magnification mode from A3 size to A4 size is set, whereas a B5 sized document is really set on the transparent plate. In this case, the optical system moves more quickly than in a normal mode since the reducing magnification mode is selected, and returns back to the home position if the exposure on the B5 sized document is complete. Therefore, it takes a long time from a time point where the light source has returned to the home position to a time point where the next paper is conveyed to the registration roller, as a result of which, the time the light source is turned on continuously at the home position becomes considerably long, causing the temperature rise in the neighbourhood of the home position to be further noticeable.
In addition to the above electrophotographic copying apparatus, there is proposed an electrophotographic copying apparatus wherein the time required for continuous copying is reduced by causing a light source to turn on preliminarily before the light source returns to the home position (Unexamined Japanese Patent Publication No. 136728/1985).
In an electrophotographic copying apparatus having a constitution such as above, wherein if the paper feeding cassettes are stacked one on top the other in the apparatus, there is no consideration given at all to prevent variation of the time required to convey the paper to the registration roller, and therefore, under a condition where a paper feeding cassette is selected whereby the time to feed the paper to the registration roller takes long, there is a high possibility that the time the light source is turned on becomes considerably longer as compared with the original lighting time of the light source, and a result of which, the temperature rise in the neighbourhood of the home position can become excessively high.